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THE OCCURRENCE AND ORIGIN OF ZABUYELITE (Li₂CO₃) IN SPODUMENE-HOSTED FLUID INCLUSIONS: IMPLICATIONS FOR THE INTERNAL EVOLUTION OF RARE-ELEMENT GRANITIC PEGMATITES

Alan J. Anderson^1,, Alan H. Clark² and Samantha Gray^1,¶

¹ Department of Geology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada
² Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada
³ Department of Geology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada

E-mail address: aanderso{at}stfx.ca

Solid – liquid – vapor fluid inclusions in spodumene in rare-element granitic pegmatites commonly contain one or more high-birefringence minerals. Optical examination and laser Raman spectroscopic analyses of over 500 crystal-rich fluid inclusions in spodumene from Bikita and Kamativi, Zimbabwe, and Bernic Lake (Tanco), Manitoba, indicate that the high-birefringence phase is zabuyelite (Li₂CO₃). Laser Raman spectra were also obtained from fluid inclusions in a wafer of spodumene from the Tanco pegmatite reported to contain the type samples of diomignite (Li₂B₄O₇). In every fluid inclusion, the high-birefringence phase was shown to be zabuyelite; no phase yielding the Raman spectrum of Li₂B₄O₇ was observed. Petrographic analysis indicates that the inclusions are secondary in origin and are trapped within healed fractures and cleavage planes. Essentially all fluid inclusions exhibit extensive necking after the crystallization of solid phases. The dominant solid phases are quartz and zabuyelite. Other minerals such as cookeite, calcite, a cesium-rich phase, apatite and several unidentified minerals were found in fewer than 5% of the fluid inclusions examined. An estimate of the bulk composition of the fluid entrapped within spodumene at Tanco was obtained by averaging the contents of several hundred coeval fluid inclusions, and the composition of individual fluid inclusions was determined using laser Raman spectroscopy, synchrotron X-ray fluorescence and laser ablation – inductively coupled plasma – mass spectrometry. The results indicate that the inclusions in spodumene, like those in the quartz component of SQUI, entrapped a low-salinity (ca. 7 wt.% NaCl equiv.), alkali-rich, aqueous carbonic fluid. We propose that the solid – liquid – vapor inclusions in spodumene from Tanco, Bikita and Kamativi are the products of a reaction between the low-density aqueous carbonic fluid and the host spodumene during the late stages of pegmatite evolution; therefore, they do not represent the products of a complex borosilicate melt as suggested previously.

Keywords: zabuyelite, lithium carbonate, granite pegmatite, spodumene, spodumene–quartz intergrowths after petalite (SQUI), daughter mineral, fluid inclusion, laser Raman spectroscopy, diomignite, Tanco, Manitoba, Bikita, Kamativi, Zimbabwe.

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